My boot scan option is disabled

Hi everyone,
this is my 1st 3d in this forum and I apologize in advance in case this is the wrong section for the following topic (and for my english too :))…

I am recently using a pc with Windows Vista Ultimate x64, and I find out that my boot scan option is disabled in Avast Menu, is this normal? I mean, I realized it only now, after 1 month (ghgh) … it is possbile that I’m under infections?

thanks in advance to everyone
bye

Yes, it’s normal. On avast 4, the boot time scanning is only available for XP\Vista 32bits.